To establish the role of N2 in the formation of HD from D2 + H2O by nitrogenase we will remove N2 from diluent and reactant gases by adsorption at -196 degrees on molecular sieve. Gas mixtures will be prepared over mercury in all glass systems to avoid contaminating N2, and these plus determined amounts of N2 will constitute gas atmospheres over purified nitrogenase systems that will be allowed to react in the presence of D2. Any HD formed will be measured (mass 3) mass spectrometrically. Neon will be employed as the inert gas. We will determine whether there is or is not an N2-independent formation of HD by nitrogenase. We will establish the extent to which Shethna FeS II protein can protect nitrogenase at different OR potentials against inactivation by O2. The system will be poised at specific potentials before exposure to O2. We will investigate the metabolism of energy-yielding compounds that support N2 fixation. Attention will be paid particularly to substrates for Rhizobium leguminosarum, Azospirillum lipoferum and Anabaena 7120. The hydrogenase from Azotobacter vinelandii will be solubilized, purified and its properties studied. Determine whether dinitrogenase is capable of binding MgATP by application of the methods we have developed to demonstrate binding of MgATP by dinitrogenase reductase.